A fixed bed multi-tube heat-exchanger type reactor provided with a plurality of reaction tubes (hereinafter, may be referred to as “fixed bed multi-tube reactor”) has been known up to now. Further, a method of vapor phase catalytic oxidation using the fixed bed multi-tube heat-exchanger type reactor has been known.
A method of packing a catalyst in the fixed bed multi-tube heat-exchanger type reactor generally involves packing by charging the catalyst from an upper portion of the reactor and allowing the catalyst to fall. However, according to this method, packed states differ for the respective reaction tubes because of reasons including: (1) the catalyst is powdered or degraded by physical impact of the catalyst charged to fall; and (2) packing time varies. To be specific, a level of powdering or degradation of the catalyst during catalyst packing differs for the respective reaction tubes. Further, long packing time results in a large packing density, and short packing time results in a small packing density. Therefore, according to a conventional packing method, the catalyst was hardly packed to provide uniform pressure states of the respective reaction tubes, particularly a pressure loss, which becomes an important factor in an oxidation reaction.
No technique exists aiming to provide a uniform pressure loss for the respective reaction tubes of the fixed bed multi-tube reactor, and methods for solving the problem (1) or (2) are proposed.
Examples of a method of suppressing powdering or degradation of the catalyst during catalyst packing include the following.
JP 2852712 B discloses a method of improving mechanical strength of a catalyst by coating the catalyst with an organic polymer compound having depolymerizing property on a surface of the catalyst. However, a uniform coating of all of the catalyst is difficult, and catalyst strength varies even if the catalyst strength increases as a whole. The coating has some effects in reducing the pressure loss, but this method is far from a satisfying method of providing a uniform pressure loss for the respective reaction tubes.
Further, JP 05-031351 A discloses a method of interposing a cord-like substance, having a shape and a thickness substantially not obstructing falling of a catalyst, inside a reactor when packing the catalyst from an upper portion of the reactor by allowing to fall. A slight effect is provided for preventing powdering or degradation of the catalyst, but an effect of catalyst packing time on packing density is unavoidable. Thus, this method is far from a satisfying method for providing a uniform pressure loss in the respective reaction tubes.
Further, JP 10-277381 A discloses a method involving packing dry ice prior to packing a catalyst by allowing to fall, packing the catalyst, and subsequently vaporizing and removing the dry ice.
Further, JP 09-141084 A discloses a method of packing a catalyst from an upper portion of a reactor involves packing a liquid substance inside the reactor, subsequently packing the catalyst, and then removing the liquid substance. However, these methods of packing the dry ice or the liquid substance in advance are far from satisfying methods industrially because post-treatment after catalyst packing involves time and effort, and handled substances may deteriorate a working environment.
On the other hand, examples of methods of controlling packing operation (time) include the following.
JP 11-333282 A discloses a method using an automatic packing machine provided with a catalyst feed conveyor and capable of controlling catalyst packing time. The patent discloses that the packing machine provides uniform packing time, allowing a uniform pressure loss in the respective reaction tubes. However, a difference in pressure loss may result depending on the catalyst, and thus, the method is far from satisfying.
Next, a fixed bed multi-tube heat-exchanger type reactor, using a heating medium for absorbing heat of reaction generated inside reaction tubes is conventionally provided with a plate for changing passage of the heating medium, called a baffle, to allow uniform flow of the heating medium inside the reactor as much as possible.
Such a fixed bed multi-tube heat-exchanger type reactor provided with a baffle did not have particular problems when a size of a plant was small. However, following problems arise when a size of the plant, that is, a reactor becomes large for increasing productivity as of today.
In other words, a non-uniform portion of a flow of the heating medium forms inside a reactor shell. A state of poor heat removal forms in part of reaction tubes among a plurality of reaction tubes inside the reactor. A localized abnormal high-temperature zone (hot spot) may form in the reaction tubes which are in a state of poor heat removal, possibly resulting in a reaction out of control.
Further, such different reaction states among the reaction tubes result in a problem of not preventing formation of reaction tubes in which a reaction becomes out of control. In addition, the different states result in problems of decreasing an yield of a target product gas and of decreasing a catalyst life.
On the other hand, an increase of raw material gas feed for enhancing the productivity results in portions where heat removal is slower than heat generation during a reaction, even with a conventional reactor of a small size. Thus, problems arise such as the above hot spots.
In other words, a conventional method for vapor phase catalytic oxidation using the fixed bed multi-tube heat-exchanger type reactor was not a method for vapor phase catalytic oxidation exhibiting satisfactory results such as effectively preventing forming of hot spots, yielding a large amount of a reaction product gas, and having a long catalyst life.
Further, the method of packing the catalyst in the reaction tubes of the fixed bed multi-tube heat-exchanger type reactor as described above generally involves using a packing funnel. The catalyst is packed by providing the reaction tubes with the packing funnel, and packing the catalyst by charging the catalyst and allowing the catalyst to fall through the packing funnel.
However, the powdered or degraded catalyst formed during transfer, transport, and handling of the catalyst is packed in the reaction tubes as well according to this method. Variations of pressure loss becomes large, which is a particularly important factor in an oxidation reaction during a production step of acrylic acid or methacrylic acid (hereinafter, may be referred to as “(meth)acrylic acid”), and thus, this method is far from a satisfying packing method for providing a uniform reaction.
Up to now, no technique is available for separating and removing the powdered or degraded catalyst in the packed catalyst during catalyst packing. The method as described above is merely proposed for suppressing powdering or degradation of the catalyst during catalyst packing.
However, those methods had problems in that powdering or degradation of the catalyst caused by vibration or impact taking place during transfer, transport, and handling of the catalyst from catalyst production to catalyst packing or the like in the reaction tubes of the fixed bed multi-tube reactor were hardly evaded. In addition, the catalyst was packed in the reaction tubes of the fixed bed multi-tube reactor together with the powdered or degraded catalyst or the like.
Further, when packing a catalyst in the reaction tubes of the fixed bed multi-tube heat-exchanger type reactor, the method as described above is employed to pack the catalyst by allowing the catalyst to fall from an upper portion of the reactor.
However, the catalyst may be powdered or degraded from physical impact during falling of the catalyst according to this method. For preventing the above, the catalyst itself must have mechanical strength above some level or the packing method must be somehow devised.
The mechanical strength of the catalyst can be improved to a certain degree by adjusting a molding pressure of the catalyst or devising operations of molding or support. However, the catalyst having enhanced mechanical strength through those techniques resulted in reducing specific surface areas of the catalyst, reducing active sites effective for a reaction, and not allowing control of pore distribution effective for reaction. Thus, problems arouse such that an yield of the target product was reduced and the catalyst was not practical.
Further, examples of the method of suppressing powdering or degradation of the catalyst during catalyst packing include the above methods disclosed in JP 2852712 B, JP 05-031351 A, JP 10-277381 A, and JP 09-141084.
However, a uniform coating of all of the catalyst is difficult for the method of enhancing the mechanical strength of the catalyst by coating the catalyst, and catalyst strength varies even if the catalyst strength increases as a whole. The coating has some effects in reducing powdering or degradation of the catalyst, but this method requires a step of coating during catalyst production and is far from a satisfying method.
The method of interposing a cord-like substance provides an effect of preventing powdering or degradation of the catalyst. However, the method requires an operation of pulling the cord-like substance upward while packing the catalyst. Effects such as extending the packing operation time or the like are unavoidable, and thus, this method is far from satisfying.
The method of packing the dry ice or the liquid substance before catalyst packing may result in post treatment taking time and effort after catalyst packing and deterioration of the working environment depending on the handled substances, and thus, is far from satisfying industrially.